Implant comprising oxidized cellulose and method for preparing such an implant

ABSTRACT

The present invention relates to an implant (10) comprising: —a substrate (1) the surface of which comprising oxidized cellulose, said oxidized cellulose having a degree of oxidation ranging from 0.0 to 1, and —a multilayer coating covering said substrate, said multilayer coating comprising at least a first layer (2) adjacent said substrate, said first layer being formed of chitosan, and a second layer (3) adjacent said first layer, said second layer being formed of oxidized cellulose having a degree of oxidation ranging from 0.5 to 1. The invention further relates to a method for preparing such an implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of PCT/EP2015/062017 filed May 29, 2015, which claims benefit of and priority to European Application Serial No. 14305820.4 filed May 30, 2014, the disclosure of the above-identified application is hereby incorporated by reference in its entirety.

The present invention relates to implants comprising a substrate the surface of which comprises oxidized cellulose and a coating applied on said substrate.

These implants may be used, for example, as haemostatic patches, adhesion prevention barriers, or as wall reinforcements in the repair, reinforcement or replacement of soft tissues.

Oxidized cellulose is of high interest in the field of medical implants. Oxidized cellulose is a highly biocompatible material, showing properties such as high moisture, handling ability which can help the repair, reinforcement or replacement of soft tissues.

Oxidized cellulose has bactericidal effects towards a wide spectrum of aerobic and anaerobic pathogens and therefore shows a therapeutic potential for use in medical implants in general.

In addition, thanks to its good haemostatic effects, biosolubility and biodegradability, antioxidant and wound-healing properties, oxidized cellulose represents a suitable means for the therapy of bleeding conditions in various fields of medicine. As such, oxidized cellulose may advantageously constitute the absorbent substrate of a haemostatic patch.

Anyway, it has been observed that non bioresorbable oxidized cellulose could trigger an undesirable immune response from the body once implanted. On the contrary, for some applications, bioresorbable oxidized cellulose degrades too rapidly in physiological conditions: the mechanical properties of the implant disappear before the implant had time to perform its intended function, thereby jeopardizing the success of the surgical operation.

For the purpose of the present application, the term “bioresorbable” is intended to mean the characteristic according to which a material is degraded by the biological tissues and the surrounding fluids, in vivo after a given period of time, that may vary, for example, from a few hours to several months, depending on the chemical nature of the material.

Haemostatic patches are implantable medical devices for stopping the flow of biological fluids such as blood during surgery. Permanent implants are not always necessary for use as haemostatic patches. For example, bioresorbable or partly-bioresorbable haemostatic patches may be made to at least partly disappear in vivo after implantation, after a few weeks for example, when their function of stopping the effusion of biological fluids is no longer necessary.

Permanent implants are neither always essential for the repair, reinforcement or replacement of soft tissues. For example, in the case of treatment of certain defects such as for the treatment of hernias or reconstruction of a visceral wall, one may seek to limit the amount of foreign bodies which remain permanently in a human body and promote tissue reconstruction.

Thus, it would be desirable to provide an implant provoking no immune response from the body once implanted, this implant having nevertheless a substrate comprising oxidized cellulose, where this oxidized cellulose would show a degradation time sufficiently delayed so that the implant would be capable of performing its intended function.

The Applicant has found that by applying a particular coating on a substrate the surface of which comprises a specific oxidized cellulose, it was possible to obtain an implant comprising oxidized cellulose capable of having a degradation time in vivo sufficient for obtaining the intended results expected from the presence of oxidized cellulose while avoiding problematic immune response from the body.

A first aspect of the invention is an implant comprising:

-   -   a substrate the surface of which comprising at least oxidized         cellulose, said oxidized cellulose having a degree of oxidation         ranging from 0.5 to 1, and     -   a multilayer coating covering said substrate, said multilayer         coating comprising at least a first layer adjacent the surface         of said substrate, said first layer being formed of chitosan,         and a second layer adjacent said first layer, said second layer         being formed of oxidized cellulose having a degree of oxidation         ranging from 0.5 to 1.

The implant of the invention is at least partly bioresorbable. In the implant of the invention, the oxidized cellulose present at least at the surface of the substrate is bioresorbable and shows a degradation time in physiological conditions compatible with the function the implant is intended to perform. The implant of the invention therefore allows providing at least partly bioresorbable implants comprising oxidized cellulose having both a significant degradation time in vivo and furthermore showing the properties of oxidized cellulose in general, such as biocompatibility, antioxidant and haemostatic properties, bactericidal properties, etc. . . . In particular, the implants of the invention show good haemostatic properties and good mechanical properties.

Another aspect of the invention is a method for preparing an implant as described herein, comprising the following steps:

-   -   i) providing a substrate the surface of which comprising at         least oxidized cellulose, said oxidized cellulose having a         degree of oxidation ranging from 0.5 to 1,     -   ii) providing a solution of chitosan,     -   iii) providing a solution of oxidized cellulose having a degree         of oxidation ranging from 0.5 to 1,     -   iv) covering said substrate with a part of the solution of         chitosan of ii) for forming a first layer adjacent the surface         of said substrate,     -   v) covering the one layer coated substrate obtained in step iv)         with a part of the solution of oxidized cellulose of iii) for         forming a second layer adjacent said first layer,     -   vi) optionally repeating steps iv) and v) as many times as         desired.

The advantages of the invention will be better understood in view of the detailed description that follows and with the help of the accompanying drawings in which:

FIGS. 1A-1E are cross section views showing the preparation of an embodiment of an implant according to the invention, with a first layer formed of chitosan and a second layer formed of oxidized cellulose,

FIGS. 2A-2B are cross section views showing the preparation of another embodiment of an implant of the invention, provided with a third layer, formed of chitosan.

The implant of the present invention comprises a substrate the surface of which comprises at least oxidized cellulose, said oxidized cellulose having a degree of oxidation ranging from 0.5 to 1.

By “degree of oxidation” of the oxidized cellulose, is meant in the present application, the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups. In particular, in the oxidized cellulose suitable for the present invention, from 50% to 100% of the oxidizable C₆ primary alcohol groups are oxidized. In embodiments where the degree of oxidation is 1, and therefore 100% of the oxidizable C₆ primary alcohol groups are oxidized, the oxidized cellulose is polyglucuronic acid.

Oxidized cellulose is a known material. Non oxidized cellulose comprises a plurality of anhydroglucose units, each anyhdroglucose unit comprising three hydroxyl groups. From these three hydroxyl groups, two of them are secondary alcohols (positioned on carbons C₂ and C₃ of the anhydroglucose unit) and one is a primary alcohol (positioned on carbon C₆ of the anydroglucose unit). In the present application, the oxidizable C₆ primary alcohol groups are the C₆ primary alcohol groups initially present in the cellulose before oxidation. Oxidized cellulose suitable for the present invention is oxidized cellulose, where the C₆ primary alcohol is partially or fully oxidized to carboxylic acid, for example to give polyglucuronic acid, and mixtures thereof. Oxidized cellulose suitable for the present invention is oxidized cellulose, where the C₆ primary alcohol groups are partially or fully oxidized to carboxylic acid groups. In particular, in the oxidized cellulose suitable for the invention, the C₂ and C₃ secondary alcohol groups are not oxidized. Because the oxidized cellulose suitable for the invention comprises carboxylic acid groups, said oxidized cellulose is negatively charged. The cellulose used for oxidation can be obtained from type I cellulose or can be regenerated.

Several types of regenerated cellulose have been developed industrially. We may mention for example the “viscose” process, which is based on the solubility of cellulose xanthate in a dilute solution of sodium hydroxide. We may also mention the so-called “cupro-ammonium process” employed for example by the company Bemberg in Italy or the company Asahi Chemical Industries in Japan, which consists of dissolving cellulose in an ammoniacal solution of copper. Another method of preparing regenerated cellulose suitable for the present invention is the method of organic-phase dissolution of cellulose by N-methylmorpholine oxide (N.M.M.O.), called the “Lyocell® process”, employed for example by the company Lenzing in Austria.

The oxidized cellulose of the substrate of the implant of the invention shows a degree of oxidation ranging from 0.5 to 1, wherein the degree of oxidation is the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups. An oxidized cellulose with such a degree of oxidation is bioresorbable. The oxidized cellulose suitable for the present invention may be prepared by oxidation of cellulose with NO₂. Oxidation of cellulose with NO₂ is a selective reaction allowing the oxidation to occur on the C₆ primary alcohol group only, so that the hydroxyl group of carbon C₆ is oxidized into a carboxylic acid group. The preparation of such an oxidized cellulose is described in WO2006/018552. The oxidized cellulose of the present invention, in particular prepared as described in WO2006/018552, is a cellulose where part or all of the C₆ primary alcohol groups are oxidized to carboxylic acid groups, said oxidized cellulose being therefore negatively charged.

Oxidized cellulose of degree of oxidation ranging from 0.5 to 1 as defined above may also be commercially available from company Ethicon under the tradename of “Surgicel®” or “Interceed®”, or from company Covidien under the tradename of “Veriset®”.

In embodiments, the oxidized cellulose suitable for the present invention present at least at the surface of the substrate of the implant of the invention shows a degree of oxidation of about 0.6 as defined above. Such an oxidized cellulose is amorphic. In embodiments, for example, when it is desired to maximize the haemostatic efficiency of the oxidized cellulose, the oxidized cellulose shows a degree of oxidation, as defined above, ranging from 0.6 to 1.

Oxidized cellulose suitable for the present invention, where the C₆ primary alcohol groups are partially or fully oxidized to carboxylic acid groups, is a compound which is naturally negatively charged. The surface of the substrate of the implant of the invention is therefore negatively charged. In this view, the substrate of the implant of the invention may optionally further comprise other biocompatible bioresorbable or non bioresorbable materials in addition to oxidized cellulose of degree of oxidation, as defined above, ranging from 0.5 to 1, as long as its surface remains negatively charged. In particular, the substrate of the implant of the invention may further comprise a neutral material or a negatively charged material.

Suitable neutral non bioresorbable materials that may be included in the substrate of the implant of the invention may be selected from polypropylene, polyethylene terephthalate and combinations thereof. Suitable neutral bioresorbable materials that may be included in the substrate of the implant of the invention may be selected from polylactic acid, polyglycolic acid and combinations thereof. Suitable bioresorbable negatively charged materials that may be included in the substrate of the implant of the invention may be selected from polysaccharides such as alginate, hyaluronan and combinations thereof.

In embodiments, the implant of the invention is bioresorbable. For example, the substrate consists in bioresorbable materials only. Apart from the oxidized cellulose of degree of oxidation, as defined above, ranging from 0.5 to 1, these bioresorbable materials may be selected from polylactic acid, polyglycolic acid, polysaccharides such as alginate, hyaluronan, and combinations thereof. In embodiments, the substrate of the implant of the invention consists in said oxidized cellulose having a degree of oxidation ranging from 0.5 to 1, as defined above, namely wherein the degree of oxidation is the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups. No other material is present in the substrate or at the surface of the substrate. In such embodiments, the implant of the invention is bioresorbable. The implant of the invention therefore shows a degradation time in vivo greater than the degradation time that would be that of the substrate taken on its own. The implant of the invention therefore allows providing fully bioresorbable implants comprising oxidized cellulose having both a significant degradation time in vivo and furthermore showing the properties of oxidized cellulose in general, such as biocompatibility, antioxidant and haemostatic properties, bactericidal properties, etc. . . .

The substrate of the implant of the present invention may show any form, shape or structure suitable for implantation inside a human or animal body, in adequation with the function the implant is intended to perform.

For example, the substrate may be under the form of porous or solid body. In a view of being used for forming either a haemostatic patch or a reinforcement wall, the substrate may preferably be under the form of a porous layer. In embodiments, the substrate is under the form of a porous layer.

In the present application, “porous layer” means a layer having pores, or voids, cells, holes, orifices, distributed regularly or irregularly, not only on the surface but also within the thickness of said layer, and more or less interconnected. Said porous layer is particularly effective for absorbing biological fluids such as blood and may be useful for forming a haemostatic patch. Such a porous layer is also effective for promoting cell colonization and may be useful for forming a reinforcement wall in hernia repair.

Such a porous layer may for example be under the form of a foam or a sponge, for example obtained by freeze-drying of a solution of oxidized cellulose, or under the form of an openwork textile.

According to the present application, “textile” means any arrangement or assemblage of biocompatible threads, fibres, filaments and/or multifilaments, for example obtained by knitting, weaving, braiding, or alternatively non-woven. The arrangement of threads of the textile according to the invention defines at least two opposite faces, a first face and a second face.

In the present application, “openwork textile” means any textile whose arrangement of threads of which it is constituted determines openings, cells or voids in the thickness of the textile and on the faces of the textile, and these openings, cells or voids can constitute channels with openings on either side of the textile. This openwork textile gives good absorption of biological fluids. Such an openwork textile also favors cell colonization.

In embodiments, the substrate is under the form of an openwork textile. The openwork textile may comprise yarns of oxidized cellulose having a degree of oxidation, as defined above, ranging from 0.5 to 1 and optionally additional yarns of biocompatible bioresorbable or non bioresorbable materials. In embodiments, the substrate consists in an openwork textile of oxidized cellulose having a degree of oxidation ranging from 0.5 to 1 as defined above, namely wherein the degree of oxidation is the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups.

The openwork textile may be in the form of a two-dimensional or three-dimensional knitted fabric.

“Two-dimensional knitted fabric” means, in the sense of the present application, a knitted fabric having two opposite faces joined together by stitches but lacking cross-members giving it a certain thickness: a knitted fabric of this kind can be obtained for example by knitting threads on a warp knitting machine or Raschel machine using two guide bars. Examples of knitting of two-dimensional knitted fabrics suitable for the present invention are given in document WO2009/071998.

“Three-dimensional knitted fabric” means, according to the present application, a knitted fabric having two opposite faces joined together by a cross-member giving the knitted fabric a significant thickness, said cross-member itself being formed of additional connecting threads supplementary to the threads forming the two faces of the knitted fabric. This knitted fabric can be obtained for example on a warp knitting machine or double-bed Raschel machine using several guide bars. Examples of knitting of three-dimensional knitted fabrics suitable for the present invention are given in documents WO99/05990, WO2009/031035, WO2009/071998.

This kind of three-dimensional knitted fabric, with the presence of a spacer giving it a significant thickness, provides excellent absorption of biological fluids such as blood and is particularly suitable for manufacture of a haemostatic patch. Such a three-dimensional knitted fabric may alternatively be suitable for the manufacture of a reinforcement wall, as its porosity and significant thickness provides for an adequate medium and space for cell colonization.

A knitted fabric, in particular three-dimensional, based on oxidized cellulose, can be obtained by knitting firstly threads of unoxidized regenerated cellulose, then submitting the knitted fabric thus obtained to oxidation.

In fact, when spun through a perforated plate, viscose sets in an acid medium and forms long continuous filaments of regenerated cellulose, which are dried and combined in multifilament threads. A regenerated cellulose thread is obtained that has good mechanical strength.

Generally this regenerated cellulose thread is not bioresorbable. However, it has good mechanical strength allowing it to be used for manufacturing a knitted fabric. As an example, we may mention, as regenerated cellulose thread suitable for manufacturing a knitted fabric suitable for the porous layer of the patch of the invention, the 90 decitex multifilament thread marketed under the name “CUPRO® Cusio” by the Italian company Bemberg.

The knitted fabric obtained is then oxidized in order to form a porous layer based on oxidized cellulose suitable for forming the substrate of the implant according to the present invention. In particular, the knitted fabric may be oxidized with NO₂ as described in WO2006/018552. Such a knitted fabric may show a high porosity allowing tissue integration and is therefore particularly useful for the repair, reinforcement or replacement of soft tissues. Such a knitted fabric also shows good tensile strength allowing it to be fixed to tissues by any known techniques, such as suturing, stitching, stapling, tacking, and combinations thereof. In addition, as a textile, such a knitted fabric is easy to handle and may further be formed in a specific desired shape.

The implant of the invention further comprises a multilayer coating covering the substrate. The multilayer coating comprises at least a first layer adjacent the surface of said substrate, this first layer being formed of chitosan, and a second layer adjacent the first layer, this second layer being formed of oxidized cellulose having a degree of oxidation ranging from 0.5 to 1 as defined above, namely wherein the degree of oxidation is the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups.

Chitosan is a biocompatible biopolymer obtained by deacetylation of chitin. Chitin is extracted from exoskeletons of arthropods such as the lobster, crab, prawn, the endoskeleton of cephalopods such as the squid, or from fungi. Extraction of chitin involves steps of hydrolysis of the proteins and lipids, depigmentation and demineralization. Hydrolysis of the proteins and lipids is usually carried out in the presence of sodium hydroxide, and demineralization requires the use of hydrochloric acid.

Once the chitin has been extracted, chitosan is obtained by a deacetylation step, which consists of hydrolysis of the acetamide groups. This reaction is generally carried out at high temperature in an alkaline solution, for example a 48% solution of sodium hydroxide (NaOH) in water, at 90° C. Chitosan is a compound that is soluble in aqueous solution and can have a degree of acetylation (DA) of up to 70%.

The following publications describe processes for deacetylation of chitin to obtain chitosan: “Lamarque, G., C. Viton, and A. Domard, New Route of Deacetylation of α- and β-Chitins by means of Freeze-Pump Out-Thaw Cycles. Biomacromolecules, 2005. 6(3): p. 1380-1388.”, “Lamarque, G., C. Viton, and A. Domard, Comparative Study of the First Heterogeneous Deacetylation of α- and β-Chitins in a Multistep Process. Biomacromolecules, 2004. 5(3): p. 992-1001.”, “Lamarque, G., C. Viton, and A. Domard, Comparative Study of the Second and Third Heterogeneous Deacetylations of α- and β-Chitins in a Multistep Process. Biomacromolecules, 2004. 5(5): p. 1899-1907.”, “Tolaimate, A., et al., Contribution to the preparation of chitins and chitosans with controlled physicochemical properties. Polymer, 2003. 44(26): p. 7939-7952.”

Chitosan is a bioresorbable compound. The degree of acetylation of chitosan can have an influence on the kinetics of degradation of chitosan. Thus, depending on the kinetics of biodegradation desired for the implant of the invention, the chitosan will have to have a degree of acetylation ranging from 0 to 70%.

In embodiments, the degree of acetylation of the chitosan is 30%.

The oxidized cellulose used for forming the second layer of the multilayer coating of the substrate of the implant of the invention may be defined in the same way as the oxidized cellulose defined above for the substrate of the implant. In particular, the oxidized cellulose used for forming the second layer of the multilayer coating of the substrate of the implant of the invention is a cellulose where the C₆ primary alcohol groups are partially or fully oxidized to carboxylic acid groups and is a negatively charged compound. This oxidized cellulose may be prepared as described in WO2006/018552. This oxidized cellulose shows a degree of oxidation ranging from 0.5 to 1, wherein the degree of oxidation is the ratio of oxidized C₆ primary alcohol groups to oxidizable C₆ primary alcohol groups, and is bioresorbable. In embodiments, this oxidized cellulose shows a degree of oxidation as defined above of 0.6. Such an oxidized cellulose is amorphic. In embodiments, the oxidized cellulose shows a degree of oxidation as defined above ranging from 0.6 to 1.

In embodiments, the multilayer coating further comprises a third layer adjacent the second layer, the third layer being formed of chitosan. The chitosan used for forming the third layer of the multilayer coating of the substrate of the implant of the invention may show the same degree of acetylation as the chitosan used for the first layer or on the contrary another degree of acetylation. The choice of the degree of acetylation of the chitosan for the first layer and of the chitosan of the third layer may depend on the desired degradation profile for the implant once implanted. An implant with a three-layer coating, namely a first layer of chitosan, a second layer of oxidized cellulose and a third layer of chitosan shows a prolonged degradation time in vivo with respect to an implant with no coating or that would be coated with one layer of chitosan only for example. It is therefore possible to provide an implant comprising oxidized cellulose and showing the properties of oxidized cellulose having in addition a delayed degradation time in vivo and therefore capable of performing its function of either a haemostatic patch or a wall reinforcement during a significant time. In particular, it is possible to provide implants comprising oxidized cellulose, having a delayed degradation time in vivo, and further showing good haemostatic properties and good mechanical properties. In further embodiments, the multilayer coating further comprises a fourth layer adjacent the third layer, said fourth layer being formed of oxidized cellulose having a degree of oxidation ranging from 0.5 to 1. In embodiments, the multilayer coating further comprises a fifth layer adjacent the fourth layer, said fifth layer being formed of chitosan. Such embodiments of the implant of the invention allow ensuring a long time performance of the oxidized cellulose present at least at the surface of the substrate.

The method for preparing the implant of the invention comprises the following steps:

-   -   i) providing a substrate the surface of which comprising at         least oxidized cellulose, said oxidized cellulose having a         degree of oxidation ranging from 0.5 to 1,     -   ii) providing a solution of chitosan,     -   iii) providing a solution of oxidized cellulose having a degree         of oxidation ranging from 0.5 to 1,     -   iv) covering said substrate with a part of the solution of         chitosan of ii) for forming a first layer adjacent the surface         of said substrate,     -   v) covering the one layer coated substrate obtained in step iv)         with a part of the solution of oxidized cellulose of iii) for         forming a second layer adjacent said first layer,     -   vi) optionally repeating steps iv) and v) as many times as         desired.

The multilayer coating of the implant of the invention is manufactured by applying the first, second and optionally third, fourth and fifth layers on the substrate by electrostatic layer-by-layer self assembly (“ELBL”). ELBL is a technique in which layers are assembled by alternating the adsorption of oppositely-charged polyelectrolytes. The process is based on the reversal of the surface charge of the coating after the deposition of each layer.

As seen above, the surface of the substrate comprising oxidized cellulose suitable for the present invention is negatively charged. Chitosan is a polycationic material and therefore a positively charged compound. A first layer of chitosan is applied on the surface of the substrate comprising oxidized cellulose as defined above. The coating of the substrate therefore becomes positively charged. A second layer, of negatively charged oxidized cellulose, as defined above, is then applied on the first layer of chitosan. The coating becomes negatively charged. A third layer, of positively charged chitosan is then applied on the second layer. The coating becomes positively charged again.

The physical basis of association is electrostatics. The application of alternately charged layers may be repeated as many times as needed.

For the manufacture of the multilayer coating as describe above, solutions of chitosan and solutions of oxidized cellulose as defined above are prepared, and the substrate may be successively covered by parts of these solutions.

The chitosan solution is generally prepared starting from a solution of chitosan in acidic water. The concentration of chitosan in said solution may range for example from 0.01% to 1%, by weight, relative to the total weight of the solution. The concentration of chitosan in the solution may depend on the molecular weight of the chitosan used. For example, for chitosan of high molecular weight, the concentration may be chosen in the low part of the range given above, so that the molecules of chitosan have enough space not to become entangled, and thereby efficiently leading to the formation of a complex between the various layers of the coating of the implant of the invention. Sodium chloride (NaCl) may be added to the solution. The pH of the solution usually ranges from 1.5 to 7.

The oxidized cellulose solution is generally prepared by dissolving oxidized cellulose as defined above in water. Caustic soda may be added to the solution. The concentration of oxidized cellulose in said solution may range for example from 0.01% to 1%, by weight, relative to the total weight of the solution. Acid, such as chlorhydric acid, may be added to the solution in order to adjust the pH from 3 to 7. The oxidized cellulose concentration is determined in function of the intended degradation profile of the layer which will be formed. Sodium chloride (NaCl) may be added to the solution.

In embodiments, step iv) comprises dipping the substrate in the solution of chitosan of ii), and step v) comprises dipping the one layer coated substrate obtained in step iv) in the solution of oxidized cellulose of iii).

The substrate is for example dipped in the chitosan solution for a determined time and then retrieved from the solution. The time during which the substrate is dipped into the solution should be sufficient for allowing the amount of solution necessary for further forming a coating to contact and attach to the negatively charged surface of the substrate. For example, this time may range from 5 to 60 minutes. In embodiments, this time is about 15 minutes. The substrate coated with this first layer is then washed, for example in water. This first layer may show a thickness ranging from 0.5 to 10 nm.

The substrate is then for example dipped in the oxidized cellulose solution for a determined time and then retrieved from the solution. Like for the first layer, the time during which the one layer coated substrate is dipped into the solution should be sufficient for allowing the amount of solution necessary for further forming a coating to contact and attach to the positively charged surface of the first layer of the now coated substrate. For example, this time may range from 1 to 60 minutes. In embodiments, this time is about 15 minutes. The substrate coated with the first and second layers is then washed, for example in water. The second layer may show a thickness ranging from 0.5 to 10 nm.

These operations may be repeated as many times as necessary, alternating the dipping of the two/three/four/ . . . -layer coated substrate in the chitosan solution and in the oxidized cellulose solution.

In other embodiments, each layer may be applied on the substrate and/or the previous layer by a brush previously dipped in the solution of the component, chitosan or oxidized cellulose as defined above, intended to be applied. For example, step iv) comprises applying on said substrate said solution of chitosan of ii) by means of a brush previously dipped in said solution of chitosan, and step v) comprises applying on said one layer coated substrate obtained in step iv) the solution of oxidized cellulose of iii) by means of a brush previously dipped in said solution of oxidized cellulose.

Alternatively, in other embodiments, each solution of a component, chitosan or oxidized cellulose as defined above, may be sprayed onto the substrate and/or previous layer. For example, step iv) comprises spraying on said substrate said solution of chitosan of ii), and step v) comprises spraying on said one layer coated substrate obtained in step iv) the solution of oxidized cellulose of iii).

The implants of the invention may be used as bioresorbable or partly-bioresorbable wall reinforcements, for example, in the repair, reinforcement or replacement of soft tissues when a permanent implant is not necessary, e.g. treatment of hernias, reconstruction of a wall, such as a visceral wall. They may also be used as haemostatic patches in order to stop blood bleeding. The implants of the invention show good haemostatic properties and good mechanical properties.

The implants of the invention may also be used in vitro as a tissue engineering product or support for culturing live cells.

The implants of the invention may also be used as a barrier against the post-surgical adhesions.

The examples that follow illustrate the invention.

EXAMPLES Example 1 Preparation of a Chitosan Solution: Solution A

0.111 g of chitosan (degree of acetylation 30%, molecular weight of 500000 g/mol) is dissolved in 100 g of water with a stoichiometric amount of acetic acid (CH₃COOH) in order to obtain a solution of chitosan at 0.1% and pH 5.

Preparation of an Oxidized Cellulose Solution: Solution B

288.7 mg of oxidized cellulose (degree of oxidation 0.6 as defined above) prepared according to WO2006/018552, is dissolved in 100 g of water together with 1.213 g of soda (NaOH). The pH of the solution is 11.8. Chlorhydric acid (HCl) at 0.2 M is added in order to obtain a solution of oxidized cellulose at 1 g/l and pH 5.

Sodium chloride (NaCl) is added to each of the solution above in order to obtain a final concentration of the component (chitosan or oxidized cellulose) in the solution of 0.25 M.

A sample textile of oxidized cellulose (degree of oxidation 0.6 as defined above), prepared according to WO2006/018552, of 3 cm×3 cm such as the textile 1 shown on FIG. 1A is provided as a substrate for preparing an implant. The textile 1 is preferably an openwork textile. The surface of the textile 1 is negatively charged. The substrate consists in said textile and is therefore bioresorbable.

The textile 1 is dipped during 15 minutes in Solution A as shown on FIG. 1B. The textile 1 is then removed from Solution A and washed during 1 min in water. This washing step is repeated twice.

A textile 1 coated with a first layer 2 of chitosan is obtained, as shown on FIG. 1C.

The surface 2 a of the first layer 2 is positively charged.

The textile 1 coated with the layer 2 of chitosan is then dipped in Solution B during 15 minutes, as shown on FIG. 1D. The textile 1 is then removed from Solution B and washed during 1 min in water. This washing step is repeated twice.

A textile 1 coated with a first layer 2 of chitosan and a second layer 3 of oxidized cellulose is obtained, as shown on FIG. 1E. This coated textile forms an implant 10 according to the invention.

A first sample of an implant 10, herein after referred to as Implant A, is kept for tests described below in Example 2.

Another sample of an implant 10 is then dipped again in Solution A during 15 minutes, as shown on FIG. 2A. The sample textile is then removed from Solution A and washed during 1 min in water. This washing step is repeated twice.

A textile 1 coated with a first layer 2 of chitosan, a second layer 3 of oxidized cellulose and a third layer 4 of chitosan is obtained, as shown on FIG. 2B. This coated textile forms another implant according to the invention, namely an implant 11. A sample of the implant 11, herein after referred to as Implant B, is kept for tests described below in Example 2.

Implant A and Implant B may be used as haemostatic patches or as adhesion prevention barriers. Implant A and B are bioresorbable.

In other embodiments not described, each layer may be applied on the textile and/or the previous layer by a brush previously dipped in the solution of the component, chitosan or oxidized cellulose, intended to be applied. Alternatively, each solution of a component, chitosan or oxidized cellulose, may be sprayed onto the textile and/or previous layer.

Example 2

In addition to Implant A and Implant B of Example 1, a non coated sample textile 1 of oxidized cellulose, such as the one of Example 1, is provided (herein after referred to as Textile A).

Implants A and B (invention) and Textile A (comparative) are immersed in a phosphate buffered saline (close to physiological fluid) solution.

After three days of immersion, Textile A has completely disappeared. On the contrary Implants A and B are still present in the phosphate buffered saline solution.

After seven days of immersion, Implants A and B are still present in the phosphate buffered saline solution.

The multilayer coated implants (Implants A and B) of the invention allow providing a bioresorbable or partly bioresorbable implant comprising oxidized cellulose, and thus showing the properties of oxidized cellulose, with a prolonged lifetime in a phosphate buffered saline solution, and thus in physiological fluids such as those present in a human body when the implant is implanted. 

The invention claimed is:
 1. A method for preparing an implant comprising: contacting a substrate having a surface including at least oxidized cellulose, said oxidized cellulose having a degree of oxidation ranging from 0.5 to 1, with a solution of chitosan to form a first layer adjacent said surface of said substrate; and covering the first layer with a solution of oxidized cellulose having a degree of oxidation from 0.5 to 1 to form a second layer adjacent said first layer.
 2. The method according to claim 1, wherein contacting the substrate with the solution of chitosan includes dipping said substrate in said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes dipping said substrate including the first layer in said solution of oxidized cellulose.
 3. The method according to claim 1, wherein contacting the substrate with the solution of chitosan includes applying said solution of chitosan by means of a brush previously dipped in said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes covering the first layer by means of a brush previously dipped in said solution of oxidized cellulose.
 4. The method according to claim 1, wherein contacting the substrate with the solution of chitosan includes spraying on said substrate said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes spraying on the first layer said solution of oxidized cellulose.
 5. A method for preparing an implant comprising: i) covering a surface of a substrate with a solution of chitosan to form a first layer on the surface of the substrate, said surface of said substrate comprising at least oxidized cellulose having a degree of oxidation ranging from 0.5 to 1; ii) covering said first layer on said surface of said substrate with a solution of oxidized cellulose to form a second layer adjacent said first layer; and iii) optionally repeating i) and ii) as many times as desired.
 6. The method according to claim 1, wherein said substrate is a porous layer.
 7. The method according to claim 1, wherein said substrate is an openwork textile.
 8. The method according to claim 1, wherein said chitosan has a degree of acetylation of 30%.
 9. The method according to claim 1, wherein said implant is bioresorbable.
 10. The method according to claim 1, further comprising covering the second layer with a solution of chitosan to form a third layer adjacent said second layer.
 11. The method according to claim 10, further comprising covering the third layer with a solution of oxidized cellulose having a degree of oxidation from 0.5 to 1 to form a fourth layer adjacent said third layer.
 12. The method according to claim 11, further comprising covering the fourth layer with a solution of chitosan to form a fifth layer adjacent said fourth layer.
 13. The method according to claim 5, wherein covering the surface of the substrate with the solution of chitosan includes dipping said substrate in said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes dipping said substrate including the first layer in said solution of oxidized cellulose.
 14. The method according to claim 5, wherein covering the surface of the substrate with the solution of chitosan includes applying said solution of chitosan by means of a brush previously dipped in said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes covering the first layer by means of a brush previously dipped in said solution of oxidized cellulose.
 15. The method according to claim 5, wherein covering the surface of the substrate with the solution of chitosan includes spraying on said surface of said substrate said solution of chitosan, and covering the first layer with the solution of oxidized cellulose includes spraying on the first layer said solution of oxidized cellulose.
 16. The method according to claim 5, wherein said substrate is a porous layer.
 17. The method according to claim 5, wherein said substrate is an openwork textile.
 18. The method according to claim 5, wherein said chitosan has a degree of acetylation of 30%.
 19. The method according to claim 5, wherein said implant is bioresorbable. 